Genetic testing to determine the presence of or a susceptibility to a disease condition offers incredible opportunities for improved medical care, and the potential for such testing increases almost daily as ever increasing numbers of disease-associated genes and/or mutations are identified. A major hurdle which must be overcome to realize this potential, however, is the high cost of testing. This is particularly true in the case of highly polymorphic genes where the need to test for a large number of variations may make the test procedure appear to be so expensive that routine testing can never be achieved.
Testing for changes in DNA sequence can proceed via complete sequencing of a target nucleic acid molecule, although many persons in the art believe that such testing is too expensive to ever be routine. Changes in DNA sequence can also be detected by a technique called "single-stranded conformational polymorphism" ("SSCP") described by Orita et al., Genomics 5:874-879 (1989), or by a modification thereof referred to a dideoxy-fingerprinting ("ddF") described by Sarkar et al., Genomics 13:4410443 (1992). SSCP and ddF both evaluate the pattern of bands created when DNA fragments are electrophoretically separated on a non-denaturing electrophoresis gel. This pattern depends on a combination of the size of the fragments and of the three-dimensional conformation of the undenatured fragments. Thus, the pattern cannot be used for sequencing, because the theoretical spacing of the fragment bands is not equal.
The hierarchical assay methodology described in U.S. Pat. No. 5,545,527 and International Patent Publication No. WO 96/07761, which are incorporated herein by reference, provides a mechanism for systematically reducing the cost per test by utilizing a series of different test methodologies which may have significant numbers of results incorrectly indicating the absence of a genetic sequence of interest, but which rarely if ever yield a result incorrectly indicating the presence of such a genetic sequence. The tests employed in the hierarchy may frequently be combinations of different types of molecular tests, for examples combinations of immunoassays, oligonucleotide probe hybridization tests, oligonucleotide fragment analyses, and direct nucleic acid sequencing.
This application relates to a particular series of tests which can be useful alone or as part of a hierarchical testing protocol for the detection and characterization of human immunodeficiency virus (HIV).